1. Field of the Invention
The present invention relates to a disk rotation driving apparatus in which a hub provided at the center of a disk-like recording medium, such as a floppy disk, is centered on a turn table.
2. Description of the Related Art
FIG. 7 is an explanatory view showing positioning between a conventional disk rotation driving apparatus and a hub mounted thereto.
In a floppy disk, a metal hub is provided at the center of a flexible disk, and a rectangular center hole 5 and a driving hole 6 are bored in this hub.
A disk rotation driving apparatus for rotating and driving the disk is provided with a turn table, and the turn table is provided with a magnet for magnetically attracting the hub, a center shaft 1 projecting from the turn table, and a driving projection 4 projecting from the turn table at a position separate from the center shaft 1.
In FIG. 7, the driving projection 4 is formed at a tip of an arm 2, and a base of the arm 2 is rotatably supported to a shaft 3 provided at a position separate from the center shaft 1 on the turn table.
When a disk is loaded, the center shaft 1 of the turn table is inserted into the center hole 5 of the hub, and almost concurrently with this, the disk is held by a magnetic head. At the point of time when the turn table starts to rotate in a clockwise direction (CW), the turn table rotates in the clockwise direction earlier than the hub because of the frictional resistance between the disk and the magnetic head, and at this time, the driving projection 4 enters the driving hole 6 of the hub. Thereafter, although the hub, together with the turn table, is rotated in the clockwise direction, since the hub receives the frictional resistance, the driving projection 4 receives a pressing force F1 in a tangential direction by a side edge 6a of the driving hole 6.
The moment M1 in the counterclockwise direction is given to the arm 2 by this pressing force F1, and a force F2 toward the outside in a radius direction is given by this moment M1 from the driving projection 4 to an outer peripheral edge 6b of the driving hole 6. The hub is pressed upward in the drawing by the force F2, so that two side edges 5a and 5b of the center hole 5 of the hub are pressed to the center shaft 1, and in this state, positioning between the turn table and the hub is performed.
Besides, a motor for rotating the turn table is provided with, for example, a pulse generator for generating one index pulse per rotation, and when the turn table reaches a predetermined rotation position, the index pulse is generated. In a control part of the disk apparatus, a control is carried out to write a signal indicating a lead-in position in the disk, while a time when the index pulse is obtained is made a reference.
As shown in FIG. 7, since the turn table and the hub are rotated in the state where the relative position is determined, the index pulse is made the reference, so that the signal can be recorded at the same position of the loaded disk.
In the disk rotation driving apparatus shown in FIG. 7, if the relative position between the center hole 5 of the hub and the driving hole 6 is always uniform, it is possible to always determine the relative position between the turn table and the hub with high precision. However, there is fluctuation in the relative position between the center hole 5 and the driving hole 6 among the hubs, and there is also fluctuation in the size of the driving hole 6. When the hub having such fluctuation is mounted on the turn table shown in FIG. 7, the relative position between the turn table and the hub can not be made constant.
For example, as shown in FIG. 7, it is assumed that the outer edge part 6b of the driving hole 6 is shifted to a position denoted by symbol 6b1 toward the outer peripheral side relative to the center hole 5. At this time, since the arm 2 rotates with the shaft 3 as a fulcrum, a press contact point Pa between the driving projection 4 and the outer edge part 6b of the driving hole 6 is moved on an arc locus Da with the shaft 3 as the center, and the press contact point is moved to Pb. As a result, a contact point between the driving projection 4 and the side edge 6a of the driving hole 6 is shifted from Ta to Ta1 by a distance xcex4.
Thus, as compared with the normal positioning state, the hub is positioned on the turn table in a state where it is rotated in the counterclockwise direction by approximately xcex4. When the signal indicating the lead-in position is recorded on the disk with the index pulse as the reference, the lead-in position of this disk becomes different from the lead-in position of another disk, and the compatibility of the disks can not be kept.
The present invention solves the foregoing conventional problems, and has an object to provide a disk rotation driving apparatus in which even if there is a deviation in a relative position between a center hole of a hub and a driving hole, when a turn table and the hub are positioned, a shift of the hub in a rotation direction can be made minimum, or the shift can be eliminated.
According to the present invention, a disk rotation driving apparatus comprises a turn table on which a hub provided in a disk is placed, a center shaft projecting at a rotation center part of the turn table, a driving projection projecting from the turn table at a position separate from the center shaft, and a motor driving part for rotating and driving the turn table, and is characterized in that
an arm including the driving projection at a tip and a rotatably supported base is provided on the turn table,
the turn table is provided with a first guide part with which an outer edge part of the base of the arm comes in contact, and a second guide part which is positioned at an inner peripheral side relative to the first guide part and with which an inner edge part of the base of the arm comes in contact, and
when a line connecting a center Od of the driving projection when the arm is at a predetermined rotation position and a center of the center shaft is made a reference normal R0, and an arc passing through the center Od of the driving projection and having a rotation center O of the arm as a center is denoted by D0,
shapes of the first guide part and the outer edge part, and shapes of the second guide part and the inner edge part are determined so that when a moment in a direction in which the driving projection goes away from the center shaft is exerted on the arm, the center Od of the driving projection is moved to a side of the reference normal R0 rather than the arc D0.
For example, the shapes of the first guide part and the outer edge part, and the shapes of the second guide part and the inner edge part are such that when the moment in the direction in which the driving projection goes away from the center shaft is exerted on the arm, the rotation center O of the arm is moved toward an outer peripheral side of the reference normal R0.
Besides, the outer edge part of the arm has a convex curve shape directed toward an outer peripheral direction, or the first guide part has a convex curve shape directed toward an inner peripheral direction, and an angle between the first guide part and the second guide part is determined so that when the moment in the direction in which the driving projection goes away from the center shaft is exerted on the arm, a contact point A between the first guide part and the outer edge part is moved toward the outer peripheral side of the reference normal R0.
For example, the first guide part and the second guide part face each other such that an interval is gradually increased toward a downstream side in a rotation direction of the turn table.
Further, when the center shaft enters a center hole of the hub, and the driving projection enters a driving hole of the hub to rotate the turn table, a resistance torque generated by sliding between the first guide part and the outer edge part and sliding between the second guide part and the inner edge part is smaller than the moment given from the driving hole to the driving projection.
The present invention is contrived such that when the driving hole of the hub pushes the driving projection and the moment is exerted on the arm, the driving projection can be moved along the reference normal R0 to the utmost degree. Thus, even if there is a positional shift between the driving hole of the hub and the center hole, the hub and the turn table can make a relative positional shift in a rotation movement direction minimum.